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Journal of Marine Biology
Volume 2012 (2012), Article ID 802875, 7 pages
http://dx.doi.org/10.1155/2012/802875
Research Article

Getting to the Point: Accuracy of Point Count in Monitoring Ecosystem Change

1Department of Biology, University of Louisiana at Lafayette, P.O. Box 42451, Lafayette, LA 70504, USA
2Littoral, Environnement et Sociétés (LIENSs), UMR 6250 CNRS, Université de La Rochelle, 2 rue Olympe de Gouges, 17042 La Rochelle, France
3Department of Biology, College of Charleston, 58 George Street, Charleston, SC 29424, USA

Received 31 May 2011; Revised 11 October 2011; Accepted 25 October 2011

Academic Editor: Ricardo Serrão Santos

Copyright © 2012 Eric Pante and Phillip Dustan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Ecological monitoring programs depend on the robust estimation of descriptive parameters. Percent cover, gleaned from transects sampled with video imagery, is a popular benthic ecology descriptor often estimated using point counting, an image-based method for identifying substrate types beneath random points. We tested the hypothesis that the number of points needed to robustly estimate benthic cover in video imagery transects depends on cover itself, predicting that lower cover will require more points/frame to be accurately estimated. While this point may seem obvious to the statistically inclined, the justification of point density has been largely ignored in the literature. We examined the statistical behavior of point count estimates using computer-simulated 20 m-long transects patterned after data from a Bahamian reef. The minimum number of points necessary to insure accurate percent cover estimation, the Optimal Point Count (OPC), is a function of mean percent cover and spatial heterogeneity of the benthic community. More points are required to characterize reefs with lower cover and more homogeneously distributed coral colonies. These results show that careful consideration must be given to sampling design and data analysis prior to attempting to estimate benthic cover, especially in the context of long-term monitoring of degrading coral reef ecosystems.